YESTERDAY'S Daily Express revealed the shocking statistic that 3,937 foreign criminals are walking the streets of Britain – because human rights law bans their deportation.

Some of them are guilty of the most appalling crimes such as child sex abuse, murder and rape.

But if you think that’s bad enough for public safety it gets even worse.

Not only are we unable to deport foreign-born criminals, we can’t even keep home-grown criminals inside prison.

You don’t need me to tell you how soft our justice system is when a caution – barely even a slapped wrist – is now the default option for so many crimes.

But even in a system as soft as ours the decision to free on day release a criminal so violent that he is known as the Skull Cracker defies belief.

When the news broke that he had absconded you no doubt wondered how on earth someone decided that he should be freed to walk the streets.

But his case is, I have to tell you, just the tip of the iceberg.

The full scandal of open prisons is deeply shocking even to those of us used to the madnesses of our system.

To recap: in 2002 Michael Wheatley, an armed robber, was given 13 life sentences at the Old Bailey.

If the story ended there that sentence alone conveys just how ridiculous our criminal justice has become.

Wheatley was given not one but 13 life sentences.

Not one of those life sentences means a thing.

Because 12 years later he was being let out on day release to prepare him for imminent permanent release.

So much for 13 life sentences.

Wheatley’s life-that-isn’t-life sentences were handed down for his raids on 13 banks and building societies over 10 months in 2001/2002.

Here’s a question: what do you think he was supposed to be doing while he was roaming the streets robbing banks?

The answer: serving a 27- year sentence for his previous robberies.

But that 27-year sentence meant diddly squat and he was soon out on parole – freed to be able to commit more crimes.

This time round Wheatley walked out of HMP Standford Hill open prison on the Isle of Sheppey, Kent, on Saturday and didn’t come back.

Jeremy Wright, the prisons minister, now says there will be a “full review”.

Don’t pin your hopes on that bringing anything other than a whitewash because we hear the same thing every time there’s a similar incident.

And the same thing happens every time: precisely nothing.

The problem is that this kind of systemic idiocy, which treats hardened criminals as if they are boy scouts acting on their honour, is endemic.

Here’s the shocker: figures released just last month show that during the past decade 106 murderers have simply walked out of their open prisons.

You read that right: one hundred and six murderers just walked out of prison.

Another 25 killers convicted of manslaughter have also escaped – well, walked – from Category D facilities since 2004.

In 2010-11 alone 17 murderers walked out.

In 2011-12 eight left and last year the figure was nine.

You might think someone would twig it’s not sensible to put convicted killers in open prisons.

But that would be too obvious a conclusion for the numbskulls in charge.

Because far from realising that what happens when you put dangerous criminals in an open prison is that they walk out, they’re actually increasing the numbers being moved to them.

Last year more than 1,240 so-called life prisoners were moved into an open prison.

That’s three times as many as the 393 moved from highsecurity prisons in 2009.

In 2012 the figure was 1,515.

TOO OPEN? Even after being convicted, many prisoners walk out of their open prison [GETTY]

Figures released just last month show that during the past decade 106 murderers have simply walked out of their open prisons

So much for the coalition getting tough on crime.

This is not just some technical issue about the best type of prison in which to hold dangerous criminals.

It poses a direct and immediate threat to public safety.

Four months ago 10 prisoners – one of whom was a killer, one an armed robber and one an arsonist – walked out of Sudbury open prison.

And the Ministry of Justice’s response wasn’t to regret this mess or promise that they’d learn from the idiocy.

It was, in that peculiarly British mix of bureaucratese, obstinacy and liberal smugness, to repeat that it was good that prisoners were transferred to an open prison: because, you see, it’s part of the “rehabilitation process”, to “test” what risk they pose.

As Jeremy Wright put it: “The purpose of any placement in open conditions is for such prisoners’ risks to be tested in less stringent conditions to inform the Parole Board’s consideration as to whether it is safe to release them into the community.”

I think most of us can answer that question for them.

We could indeed have answered it without the need for any prisoners to have been moved to an open prison to find out.

The answer is “a big risk”.

Which the prisoners then proved by walking out.

As for Wheatley’s temporary home, Standford Hill Prison – his very temporary home – it’s less than a year since murderer Michael Bruce walked out to stay with a friend.

A few months before that three prisoners left in one week.

Now Wheatley has joined the roll-call of guests of Her Majesty who have decided they’d rather leave.

Horrifically violent he may have been, sentenced to 13 life terms, but for the officials who run our criminal justice system he was the perfect candidate to be let out on day release.